As a technology for improving performance of a wireless communication system, beamforming is provided. Beamforming is a technique for increasing a signal reception strength for a specific receiver by giving directivity to a beam using multi-antennas. Beamforming is classified into transmission beamforming and reception beamforming according to which apparatus performs the beamforming. In this case, when a mobile station gets out of a serving cell and enters another cell, a handover procedure is performed. When base stations perform the beamforming, there is a problem of determining which beam is an optimal beam in a target base station.
As a handover procedure considering beams, a method for using the statistics of inter-beam handover success rates has been proposed as illustrated in FIG. 1. FIG. 1 illustrates a concept of handover using the statistics of inter-beam handover success rates in a wireless communication system. According to the handover method illustrated in FIG. 1, an administrator that manages a plurality of base stations directly controls the inter-beam handover of different base stations. Since the terminal does not know the narrow beam situations of all neighboring base stations, the administrator manages the inter-beam handover success rates using a lookup table 110. The administrator enables the terminal to perform a handover to an optimal target beam according to the success rates using the lookup table 110.
As another handover procedure considering beams, a method for using different beam widths has been proposed as illustrated in FIGS. 2A and 2B. FIGS. 2A and 2B illustrate a concept of handover using different beam widths in a wireless communication system. Referring to FIGS. 2A and 2B, a terminal receives a reference signal and determines a handover based on a channel quality measured through the reference signal. In this case, the reference signal for scanning is transmitted on a sector beam 201. A communication service is provided on a narrow beam 202.
Among the above-described handover methods, the method illustrated in FIG. 1 has an advantage in that the terminal is able to perform a handover without measurement for the narrow beam of a neighboring base station. However, there is a burden in that the administrator needs to manage handover success rates with respect to the beams of all base stations. In the method illustrated in FIGS. 2A and 2B, the terminal needs to transmit an uplink pilot signal to the base station with respect to narrow beam candidates. Therefore, as the number of narrow beam candidates increases, power consumption for determining an optimal narrow beam increases in a terminal.
Therefore, there is a need for an effective handover procedure considering beams.